The present invention relates to power limiting apparatus and, in particular, to equipment for establishing a duty cycle scaled to correspond with the measurement cycle of a peak demand meter.
It is known to reduce the duty cycle of power supplied to an air conditioning system to reduce the peak demand required from utility lines. However, these systems have not considered the advantage of scaling the repetition rate of the switching to complement a peak demand meter. Such a peak demand meter measures over successive intervals of a predetermined duration the highest amount of energy consumed during the intervals. The highest energy demanded during these intervals is used by the utility to set the billing rate to the consumer. Unfortunately, a consumer who uses very little energy overall but occasionally requires a high peak power input may be billed at a substantially higher rate than heavier users.
Known demand limiting systems generally require a continual potential across the affected lines for proper operation. Therefore, these known systems cannot be connected into a pair of lines that run to the thermostatic switch of an air conditioning system. When the thermostatic switch is closed, there is no potential across the associated lines and, therefore, no potential is present for driving this demand limiting system.
Another consideration is switching of load more rapidly than they can tolerate. For example, once an air conditioning compressor is turned off, it must remain off for a minimum time interval to allow release of fluids trapped therein. Premature operation can cause extreme stress and damage.
Accordingly, there is a need for a simple and effective system which limits the peak power demands measured by a given demand meter and which can be connected to various points in the load circuit.